The present invention relates generally to subterranean pipe string joint locators, and specifically to an apparatus and method for locating joints in coiled tubing operations.
In the drilling and completion of oil and gas wells, a wellbore is drilled into the subterranean producing formation or zone of interest. A string of pipe, e.g., casing, is typically then cemented in the wellbore, and a string of additional pipe, known as production tubing, for conducting produced fluids out of the wellbore is disposed within the cemented string of pipe. The subterranean strings of pipe are each comprised of a plurality of pipe sections which are threadedly joined together. The pipe joints, often referred to as collars, are of an increased mass as compared to other portions of the pipe sections.
After a well has been drilled, completed and placed in production, it is often necessary to service the well using procedures such as perforating, setting plugs, setting cement retainers, spotting permanent packers, reverse circulating fluid and fracturing. Such procedures may be carried out by utilizing coiled tubing. Coiled tubing is a relatively small flexible tubing, usually one to three inches in diameter, which can be stored on a reel when not being used. When used for performing well procedures, the tubing is passed through an injector mechanism, and a well tool is connected to the end of the tubing. The injector mechanism pulls the tubing from the reel, straightens the tubing and injects it through a seal assembly at the wellhead, often referred to as a stuffing box. Typically, the injector mechanism injects thousands of feet of the coiled tubing with the well tool connected at the bottom end into the casing string or the production tubing string of the well. A fluid, most often a liquid such as salt water, brine or a hydrocarbon liquid, is circulated through the coiled tubing for operating the well tool or other purpose. The coiled tubing injector at the surface is used to raise and lower the coiled tubing and the well tool during the service procedure and to remove the coiled tubing and well tool as the tubing is rewound on the reel at the end of the procedure.
During such operations, it is often necessary to precisely locate one or more of the pipe joints of the casing, a liner or the production tubing in the well. This need arises, for example, when it is necessary to precisely locate a well tool, such as a packer, within one of the pipe strings in the wellbore. A joint locator tool may be lowered into the pipe string on a length of coiled tubing, and the depth of a particular pipe joint adjacent to or near the location to which the tool is positioned can be readily found on a previously recorded casing joint or collar log for the well. However, such joint locator tools often do not work well in many oil field operations such as reverse circulating and fracturing. What is needed therefore, is a joint locator tool that can work in reverse circulation or fracturing operations.